Storage-stable iminodisuccinate solutions

ABSTRACT

The present invention relates to a process for the preparation of storage-stable iminodisuccinate solutions, by subjecting an aqueous solution of iminodisuccinate having an ammonia content of less than 20 ppm to thermal treatment at 40 to 120° C. for 5 hours up to 300 days and subsequent distillation at &lt;120° C.

The present invention relates to a process for the preparation ofstorage-stable iminodisuccinate solutions, by subjecting an aqueoussolution of iminodisuccinate having an ammonia content of less than 20ppm to thermal treatment at 40 to 120° C. for 5 hours up to 300 days andsubsequent distillation at <120° C.

The preparation of iminodisuccinate or iminodisuccinic acid and saltsthereof belong to the prior art.

According to GB-A 130 6 331, iminodisuccinate is obtained by reactingthe starting materials maleic acid and ammonia at 60 to 155° C.

According to SU-A 0639863, iminodisuccinate is obtained by reacting thesame starting materials in the presence of alkali metals at 110-130° C.

WO-A 98/45251, finally, discloses the synthesis of iminodisuccinic acidalkali metal salts by reaction of maleic anhydride, alkali metalhydroxide, NH₃ and water, the reaction mixture being admixed withfurther water and, if appropriate, methanol, and being freed from NH₃ bydistillation at 50 to 170° C. and 0.1 to 50 bar.

A disadvantage of the processes of the prior art is the fact that theproduct comprises considerable amounts of ammonia due to the process.Even the distillation in WO-A 98/45251, which has complex apparatusrequirements, is not able to reduce the ammonia in the long term, sothat the use of iminodisuccinates have hitherto been possible only underrestrictions.

However, applications such as textile cleaning, domestic cleaning andcosmetics require a storage-stable iminodisuccinate free from emissionsof NH₃ gas which originate from decomposition of the iminodisuccinate orof NH₃ production residues.

It is an object of the present invention, therefore, to find a processfor the preparation of storage-stable iminodisuccinate solutions whichmakes it possible to store iminodisuccinate solutions for a long periodwithout formation of ammonia and as a result makes possible theapplication in the abovementioned sectors.

Surprisingly, it has now been found that an iminodisuccinate solutionwhich has been heated for a plurality of hours then forms significantlyless ammonia than a correspondingly solution which has not beenthermally treated. At the same time, an iminodisuccinate solution, afterthe heating, has a higher content of iminodisuccinate, than before theheating. It is possible as a result to obtain a product of significantlyhigher purity and better odour properties. Although iminodisuccinate istemperature-sensitive and heating the solution leads to chemicaldecomposition with the formation of ammonia, in the context of thepresent invention, it has been found that, by specifically meteredsupply of heat, higher product quality can be achieved with respect tostability of the iminodisuccinate solution against progressivedecomposition and ammonia formation.

The solution, and thus object of the present invention, is a process forthe preparation of a storage-stable solution of iminodisuccinate havingan ammonia content <50 ppm, characterized in that an iminodisuccinatesolution having an elevated ammonia content is thermally treated at 40to 120° C. for 5 hours up to 300 days and is then subjected to adistillation at temperatures <120° C.

Thermal treatment in the context of the present invention means heatinga substance, here an iminodisuccinate solution having elevated ammoniacontent, for a relatively long period. An elevated ammonia content inthe context of the present invention and as is present in the product asa result of the iminodisuccinate syntheses of the abovedescribed priorart, means 50 to 500 ppm. In particular as a result of storage ofiminodisuccinate solutions, as are obtained according to the processesdescribed in the prior art, an increase of the ammonia concentrationcontinuously up to values up to 150 ppm in the course of 200 days may beobserved (FIG. 1).

An iminodisuccinate solution which has been, according to the invention,thermally treated at 90° C. and then subjected to a distillation,prepared by the abovementioned processes of the prior art, has formedonly 35 ppm of ammonia after 200 days (FIG. 1).

The finding that a thermal treatment of the iminodisuccinate solutionleads to better product properties is surprisingly in contrast to theobservation that an iminodisuccinate solution loses concentration whenit is heated.

Iminodisuccinate solutions in the context of the present invention areaqueous solutions of iminodisuccinate, preferably 0.1 to 40% strength byweight aqueous solutions, but also mixtures of these aqueous solutionswith organic solvents, for example alcohols. Alcohols which may bementioned by way of example are methanol, ethanol, propanols, butanols.

The invention preferably relates to a process for the preparation ofstorage-stable solutions of iminodisuccinate having an ammonia content<50 ppm, characterized in that an iminodisuccinate solution havingelevated ammonia content is thermally treated at 40 to 120° C.,particularly preferably at 80 to 115° C., for 10 to 100 hours,particularly preferably 15 to 70 hours, and is then subjected to adistillation at temperatures of 40 to 130° C., particularly preferablyat 60 to 120° C.

A procedure is followed in such a manner that, after preparation of theiminodisuccinate solution, this is heated to temperatures of 80 to 120°C. and kept at these temperatures for 5 to 200 h, with mixing of thesolution. This can be performed continuously or batchwise. In the caseof the continuous procedure, suitable apparatuses can be selected andconnected so that the said residence times at the said temperatures areachieved. For this, in chemical and thermal process engineering, anumber of advantageous apparatuses and apparatus connections, forexample the kettle cascade, the tubular reactor, heat exchangersequipped with internals or the cascaded column are known.

In a subsequent step, the ammonia distillation is then carried outcontinuously or batchwise. To carry out this distillation step,appropriate apparatuses and distillation designs are known to thoseskilled in the art.

By means of this procedure, iminodisuccinate solutions can be obtained,the ammonia content of which does not exceed 35 ppm without furtherpost-treatment, even after a time period of several hundred days (FIG.1).

In accordance with the inventive process, storage-stableiminodisuccinate solutions are obtained having an ammonia content lessthan 50 ppm, preferably less than 40 ppm, particularly preferably lessthan 20 ppm, even less than 5 ppm!

Such low ammonia concentration over a period of up to 200 days nowallows the use of the storage-stable iminodisuccinate solutions incosmetics, laundry detergents, cleaning compositions, in domesticcleaning, in paper manufacture, in bleaching processes and in textiletreatment.

EXAMPLE

After preparation of the iminodisuccinate solution (obtained inaccordance with WO-A 98/45251) this was heated in the reaction kettle to102° C. and kept at this temperature for 20 hours with stirring. Ammoniaand water were then distilled off overhead from the solution in adistillation column at atmospheric pressure. In the course of this,temperatures resulted in the bottom of 105 to 106° C. At the top of thecolumn a temperature of 99° C. was established.

After the end of the experiment, the ammonia content in the distillediminodisuccinate solution was below the limit of detection of 2 ppm.After 8 weeks, the ammonia content had increased to 16 ppm.

1. Process for the preparation of storage-stable solutions ofiminodisuccinate having an ammonia content of <50 ppm, characterized inthat iminodisuccinate solutions having an ammonia content greater than50 ppm are thermally treated at 40 to 120° C. for 5 hours up to 300 daysand are then subjected to a distillation at temperatures <120° C. 2.Process according to claim 1, characterized in that the thermaltreatment is carried out at 80 to 115° C.
 3. Use of the storage-stableiminodisuccinate solutions prepared according to claim 1 for cosmetics,laundry detergents, cleaning compositions, domestic cleaning, in papermanufacture, in bleaching processes and in textile treatment.